PROJECT SUMMARY Altering the course of the global AIDS epidemic will likely require the implementation of means to prevent the transmission of human immunodeficiency virus (HIV-1). With no practical HIV-1 vaccine on the horizon, modalities that would allow women to protect themselves from sexually acquired HIV-1 infection could exert an immediate and significant impact on global HIV-1 incidence. An attractive prophylactic approach involves the interruption of virus entry into the host cell, the earliest event in the HIV-1 life cycle. Small-molecule CD4- mimetic compounds (smCMCs) bind within a conserved pocket on the HIV-1 envelope glycoprotein (Env) spike and block the entry of the virus into the cell. In addition to interfering with the binding of HIV-1 to the CD4 receptor on the target cell, smCMCs also induce conformational changes in Env, irreversibly inactivating its function. The binding of smCMCs also renders Env susceptible to inhibition by antibodies that can be elicited by currently available HIV-1 Env vaccine candidates. Thus, in addition to their direct antiviral effect, smCMCs can potentially synergize with vaccine-elicited antibodies to neutralize incoming HIV-1. In this proposal, we will formulate a newly developed smCMC for sustained vaginal delivery via a pod- intravaginal ring. The design parameters of the pod-intravaginal ring will be modified to optimize the release of the smCMC. We will evaluate the vaginal delivery of the smCMC, as well as systemic absorption and potential side effects, in monkeys. We will then examine the ability of the optimized pod-intravaginal ring delivering a smCMC, alone or in combination with an Env-elicited antibody response, to protect monkeys from multiple low- dose intravaginal challenges with a simian-human immunodeficiency virus (SHIV). Establishing the ability of the pod-intravaginal ring to deliver protective concentrations of the smCMC to the vaginal mucosa of monkeys in a sustained manner will set the stage for clinical testing of this prophylactic approach in women.